Testing and measuring circuit



May 30, 1961 M. H. DIEHL TESTING AND MEASURING CIRCUIT Original FiledSept. 15. 1955 TUNED AMP.

PHASE SUBCARRIER SPL'TTER GENERATOR E m L Y A L E D FIG.2.

INVENTORI MAX H. DIEHL, MW

HI A TORNEY.

United States Patent ()fiice 2,986,700 Patented May 30, 1961 TESTING ANDMEASURING CIRCUIT Max H. Diehl, Syracuse, N.Y., assignor to GeneralElectric Company, a corporation of New York Continuation of applicationSer. No. 534,507, Sept. 15, 1955. This application Apr. 23, 1958, Ser.No. 730,403

2 Claims. (Cl. 32485) of which, with respect to the color sub-carrierburst of reference phase, determines the hue of the color. The colorsub-carrier wave is made up of two components, an in-phase or Icomponent and a quadrature-phase or Q component. The in-phase or thequadrature phase terminology has reference to the phase of thesub-carrier burst. To obtain proper color rendition in color televisionsystems, it is essential that the I component be in phase quadraturewith respect to the Q component.

Applicant's invention is directed to the provision of simple andeffective means for eflecting such an alignment.

Another object of the present invention is to provide improvements inaligning means for color television systems.

It is also an object of the present invention to provide improvements inelectronic testing circuits.

In an illustrative embodiment for carrying into effect applicantsinvention, there is provided means for developing second harmonicvoltages from each of a pair of voltages of sub-carrier frequency. Thesecond harmonic voltages are combined to produce an output. Means arefurther provided for adjusting the phase of one of said carrier wavesuntil said output is a minimum. When such a condition exists, thefundamental components are in quadrature phase.

The novel features which I consider to be characteristic of my inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof may be bestunderstood by reference to the following description taken in connectionwith the accompanying drawings in which:

Figure 1 is a schematic diagram of a circuit for carrying out thepresent invention; and

Figure 2 is a graph of the fundamental and second harmonic components ofa pair of waves for illustrating the principle of applicants invention.

Referring now to Figure 1 of the drawing, there is shown a portion ofthe circuit that would be included in the transmitting portion of acolor television system and which functions to develop a pair ofsub-carrier waves in phase quadrature with respect to one another, onebeing modulated by the I color component from the television colorcamera and the other modulated by the Q color component from thetelevision color camera. These functions are effected by the I modulatorcomprising electron discharge devices 3 and 4 and the Q modulatorcomprising electron discharge devices 5 and 6. To the I and Q modulatorsare applied sub-carrier voltages of proper phase developed from thedelay line 7 which is in turn excited by the sub-carrier generator 8.

The sub-carrier generator 8 may include any of a variety of oscillatorgenerators, including crystal oscillators, for developing a wave ofsub-carrier frequency, which according to present-day standards is 3.58megacycles. The output of the sub-carrier generator is applied to point15 on the delay line 7 which is schematically shown as consisting of aninductive element 11 and a series of capacitive elements 12 distributedalong the length of the inductive element 11. The ends of the delay lineare terminated by respective terminating resistances 13 and 14 whichfunction to minimize reflections from the lines. Intermediate point 15on delay line 7 will be denoted as the zero phase of the delay line. Thephase of the voltage appearing at this point is arranged to be in phasewith the color reference burst or in some fixed relationship withrespect to it. Point 16 on the delay line is arranged to have a 180delay with respect to the voltage at point 15 at the sub-carrierfrequency and similarly points 17 and 18 are arranged to have and 270delays, respectively. Conductors 19, 20, 21 and 22 are connected topoints 15, 16, 17 and 18, respectively, and for the purpose ofadjustment and convenience, these connection are shown as variable.

The I modulator 1 comprises electron discharge devices 3 and 4. Device 3includes a cathode 23, a grid 24, a screen grid 25, a suppressor grid 26and a plate 27. Device 4 includes a cathode 28, a grid 29, a screen grid30, a suppressor grid 31 and an anode 32. The anodes 27 and 32 areconnected together and through anode load resistance 33 to the positiveterminal of source of unidirectional supply potential 34. Cathodes 23and 28 are connected together and through cathode load resistance 35 tothe negative terminal of source 34. Grid 26 is connected over conductor20 to point 16 on delay line. Grid 31 is connected over conductor 19 topoint 15 on delay line 7. Screen grids 25 and 31 are connected togetherand to the positive terminal of source 58, the negative terminal ofwhich is connected to ground. The phase splitter 9 comprises electrondischarge device 36, including a cathode 37, a control grid 38 and ananode 39. The cathode 37 is connected through cathode load resistance 40to the negative terminal of source 34. The anode 39 is connected throughanode load resistance 41 to the positive terminal of source 34. The grid38 is connected to terrninal 42 to which is applied the modulatingcomponent of the color signal. The anode 39 is coupled through couplingcapacitor 43 to the grid 24. Cathode 37 is coupled through couplingcapacitor 44 to the grid 29.

It should be noted that sub-carrier wave and the modulating video signalare applied to the devices 3 and 4 in push-pull relationship.Accordingly, neither carrier wave nor the modulating video wave appearin the output of the modulator. However, the modulation productscorresponding to side band components of the modulated wave do appear inthe output across load resistance 33. Balanced modulators of the kinddescribed are well-known in the art.

The Q modulator 2 and the phase splitter 10 are similar to the Imodulator 1 and the phase splitter 9 and will not be described in detailand their functions are identical thereto except that the sub-carrierwaves, applied to the Q modulator over conductors 21 and 22, are 90 outof phase with respect to the sub-carrier waves applied to the Imodulator over conductors 19 and 20, respectively. The Q component ofvideo signal is applied at the input terminals of the phase splitter 10.The anodes of the devices 5 and 6 are connected together with the anodes27 and 32 of the I modulator. Thus, across the anode 33 is obtained Iand Q sub-carrier components of the color television signal.

It will be apparent that the I and Q modulators are not perfect andinclude non-linearities which give rise to harmonic components ofvoltage. Accordingly, across the load resistance 33 are obtained secondharmonic voltages of the carrier voltages applied to these modulators.Conventionally, the output from the balanced modulators are applied incommonly used systems to a band-pass filter 45 which restricts the sideband components to those occuring in the 2 to magacycle range. Thisband-pass filter may take the form of an inductance-capacitance filtercircuit having the desired band-pass characteristic. The I and Qsub-carrier components obtained from the bandpass filter are thencombined in the adder stage 46 with the luminance component of thetelevision signal, the synchronizing signal and the color burst. Theoutput from the adder 46 in conventional systems is applied to thetelevision transmitter. At this point, applicant has provided a tunedamplifier 47 to which is also applied the output from the adder 46,tuned to eliminate all waves except those in the vicinity of twice thesub-carrier frequency, that is, those frequencies in the vicinity of 7.2magacycles.

The tuned amplifier 47 comprises an electron discharge device 48,including a cathode 49, a grid 50, a screen grid 51, a suppressor grid52 and an anode 53. The cathode is connected through cathode loadresistance 54, bypassed by capacitance 55 to the negative terminal ofsource 34. The grid is connected through grid lead resistance 56 toground and through coupling capacitor 57 to the output of adder 46. Thescreen grid is connected to the positive terminal of source 58.Suppressor grid 52 is connected to the cathode 49. The anode 53 isconnected through parallel resonant circuit 59 to the positive terminalof source 34. The resonant circuit 59 is tuned to pass sub stantiallyonly those waves having frequencies in the vicinity of 7.2 megacycles,approximately twice the sub-carrier frequency. Between anode 53 andground, a pair of capacitances 60 and 61 are connected in series. Thejunction of these capacitances is connected to the input terminal 62 ofoscilloscope 67, the other terminal of the oscilloscope being connectedto ground. Applicants tuned amplifier 47 may just as conveniently havebeen connected to the output of the I and Q modulator directly.

The operation of applicants invention will be more fully appreciated byconsidering Figure 2 wherein there is shown a graph of voltages plottedon amplitude versus time scale. The graph 63 represents the voltageappearing between points 15 and 16 and is the voltage applied to the Imodulater. The graph 64 represents the voltage appearing betweenterminals -17 and 18 and is the voltage applied to the Q modulator. Thegraph 65 is the component of second harmonic voltage developed at theoutput of the I modulator. This second harmonic component is in phasewith the fundamental component 63. Similarly, the graph 66 representsthe second harmonic component of voltage developed at the output of theQ modulator and similarly, it is in phase with the fundamental component63. It will be understood that the second harmonic components of thevoltage have been shown of much larger amplitude with a reference to thefundamental component than would normally be the case. This has beendone for the purpose of clarity and emphasis. From Figure 2, it isapparent that when waves 63 and 64 are in phase quadrature, secondharmonic components 65 and 66 are out of phase and cancel one another.In accordance with applicants invention, the oscilloscope 67 is adjustedto have a sweep suitable for obtaining an indication of the amplituderesponse of the signal applied to its input terminals, then phase of thewave appearing on conductors 21 and 22 is adjusted with respect to thephase of the wave appearing between points 15 and 16 until a minimalindication is obtained on the oscilloscope, at which time the waveapplied to the I modulator will be in phase quadrature with respect tothe wave applied to the Q modulator as will be apparent from Figure 2.

While a particular embodiment of my invention has been shown anddescribed, it is apparent that changes and modifications may be madewithout departing from the invention in its broader aspects and,therefore, the aim in the appended claims is to cover all such changesand modifications which fall within the true spirit and scope of myinvention.

What is claimed is:

1. In a circuit including a balanced modulator to which are applied apair of carrier voltages in quadrature phased relationship and fromwhich is inherently obtained a small amount of second harmonics of theapplied carrier voltages, means for determining whether the phases ofsaid carrier voltages are in phase quadrature comprising a single tunedamplifier selectively responsive to and amplifying said second harmonicsof the applied carrier voltages and oscilloscope means for visuallyindicating the phase of one of said carrier waves with respect to theother to determine whether a substantially straight line is presented toindicate maximum cancellation of opposing second harmonic voltages andtherefore exact phase quadrature of said carrier voltages with respectto each other.

2. Apparatus for determining when a pair of carriers at the samefrequency but desired in quadrature phase relationship with each otherare in such quadrature phase relationship comprising an amplifier, saidamplifier having an anode and a control electrode, means to couple thesignals to said control electrode, a tuned circuit resonant to thesecond harmonics of the signals, a first and a second capacitor inseries disposed between said tuned circuit at the end opposite the anodeconnected end and ground, an oscilloscope, a lead connected between thejunction of said capacitors and the input of said oscilloscope, saidamplifier and associated circuit forming a tuned amplifier, whereby whena straight line is presented on said oscilloscope this will indicatemaximum cancellation of opposing second harmonic voltages and thereforephase quadrature of said carrier voltages.

References Cited in the file of this patent UNITED STATES PATENTS2,209,064 Nyquist July 23, 1940 2,333,322 Levy Nov. 2, 1943 2,455,646Beard et al. Dec. 7, 1948 2,476,977 Hansel July 26, 1949 2,522,369Guanella Sept. 12, 1950 2,580,803 Logan Jan. 1, 1952 2,659,050 HoneyNov. 10, 1953 2,695,399 Martin Nov. 23, 1954 2,713,661 Schmitt July 19,1955 2,902,650 Kaiser Sept. 1, 1959 OTHER REFERENCES Use of theVectorscope Technique to Service Color TV, article in ElectronicTechnician, pages 34-37, August 1957.

